The present invention relates to an electronic sensing device operable to actuate a household lighting fixture in response to a sensed environmental condition, such as sound or movement within a room.
It is generally known to provide switch means actuated by a sensed environmental condition such as sound or movement within a room. The U.S. Patent to Stetner, U.S. Pat. No. 4,103,294, discloses a sound actuated switch which is wired in parallel with a household light switch to act as a burglar alarm. The Stetner device employs an SCR trigger and a timer to maintain the lights on for a set period of time after the device senses a noise and triggers the alarm.
U.S. Patent to Ott, U.S. Pat. No. 3,582,671, relates to a sound responsive lighting arrangement which also employs an SCR trigger. The Ott device detects the level of sound in the room, and as the sound level decreases to a point below a pre-determined level, the device turns off the light fixture.
U.S. Patent to Otani, U.S. Pat. No. 4,106,003, discloses a burglar alarm system which utilizes an ultrasonic wave transmitting oscillator and receiver. The ultrasonic transmitter is placed in the protected room, and the receiver detects change in the ambient ultrasonic sound field. The Otani device times the duration of the changes so that changes having a duration of less than a particular time will be ignored.
U.S. Patent to Hossbach, U.S. Pat. No. 3,898,640, discloses a burglar alarm having an ultrasonic transmitter, and an ultrasonic receiving device which detects changes in the natural resonance frequency of the protected room. In this manner, the Hossbach device will ignore movements within the room itself, but will detect changes in the room dimensions due to the opening of a window or door.
While these prior art switching devices switch on either a light fixture or an alarm device in response to a sensed environmental condition, the prior art devices are powered through the use of an external power source. This causes problems and increased power consumption and further inconvenience in that the alarm device must be powered separately from the alarm or light fixture. Furthermore, the prior art devices do not disclose the concept of providing a timer circuit which is automatically reset or updated in response to continued activity within the room, therefore leading to the premature switching off of the device.